The present invention generally relates to a fail-safe port apparatus for use with an optical fiber and, in particular, relates to one such port apparatus having means, employing a liquid crystal material, for switching a light beam between first and second light paths such that losses are minimized.
Currently, many communications systems are being implemented using optical fibers as the primary system transmission medium. Such applications are most frequently directed to communications networks that are local in nature, such as, for example, a local area network (LAN). As known, a LAN is, essentially, a communication network particularly adapted for providing networking facilities to a relatively small geographical area, for example, a corporate or university facility. One major difference between, for example, a long distance communication network and a local area network, at least with respect to the use of optical fibers, is that the long distance network usually requires a comparatively high powered laser, whereas a local area network can operate by use of a comparatively low powered light emitting diode transmitter. Nevertheless, in optical local area networks, in order to avoid the use of the expensive high power lasers and enhance the use of less expensive low power light emitting diodes, the light signal is usually regenerated along the network to compensate for losses due to the signal attenuation in the optical fiber and associated hardware. Frequently, a signal regenerator is provided at each local area network access port.
At the present time, access to such ports is most frequently accomplished by means of a directional coupler that, in essence, includes a local port receiving fiber fused to the primary, or system, transmission optical fiber and connected to a light receiver. One difficulty with such optical couplers is that considerable losses are sustained by signals traversing thereacross. Characteristically, each such coupler can introduce between 3 to 8 db loss. Hence, in typical local area networks the optical signals need to be regenerated along the transmission medium, usually at each port. However, if a failure occurs at one or more consecutive ports along the transmission fiber, or if a number of consecutive ports are unused, the signal strength rapidly decreases. This signal strength loss occurs because the coupler loss occurs regardless of whether or not the port is active. Further, in the event of a port failure it is possible, since the coupler remains in the transmission medium, for signal reflections to be generated and thus reduce the purity of the signal on the system optical fiber.
Alternatively, the need for signal regeneration may be reduced by providing fewer ports per fiber and/or increasing the signal strength. Nevertheless, optical directional couplers are generally considered necessary to provide a fail-safe mechanism for interconnecting to the system optical fiber transmission line. By fail-safe, it is meant that, should a local occurrence at the port result in a failure thereat, the remainder of the ports coupled to the main transmission medium would be substantially unaffected. This is necessitated to avoid a catastrophic system failure due to a purely local failure event.
Consequently, it is highly desirable to provide a low loss fail-safe port for interfacing with the system optical fiber transmission medium of an optical communication network, such as, an optical local area network.